Preventing the non-specific protein adsorption and cell adhesion on biosensors, biomedical devices, and implants is crucial for the performance of these devices.1,2 Many strategies to prevent such non-specific protein adsorption and cell adhesion have been developed. For instance, a variety of polymers have been used to reduce protein, cell and bacterial adsorption at interfaces with biological tissues. Of these, poly(ethylene glycol) (PEG) is one of the most promising synthetic polymers to confer protein and cell resistance to devices having PEG immobilized onto the surface.3 
Although ethylene glycol may be block-copolymerized with other hydrophobic polymers to enable surface immobilization of PEG via adsorption of the hydrophobic copolymer blocks,4-6 a covalent attachment to the substrate is preferable for long term stability of PEG surface coatings. For that reason, a number of strategies have been developed to immobilize PEG onto the surfaces of biomaterials. The most frequently employed techniques are surface graft, including “graft to” and “graft from” methods. Thiol-terminated PEG self-assembly on gold7-12 and PEG-silane reaction on the surfaces of indium tin oxide, silica and silicon13-17 are typical “graft to” techniques. Polymerizable PEG monoacrylates are often employed to graft and polymerize from a surface with immobilized initiators.18-24 PEG-bearing amine groups were also coupled with poly(N-hydroxysuccinimidyl methacrylate) films, hydrolyzed poly(methyl methacrylate) or silanized glass slides bearing aldehyde groups, respectively.14, 25-29 Polyethylene glycols containing alkyne and cyclodiene terminal groups have also been grafted onto a N-(e-maleimidocaproyl) functionalized glass slides via an aqueous Diels-Alder reaction.30 Bonding of PEG-biotin derivatives onto an avidin surface was performed,31,32 and isocyanate-terminated star PEG was employed for preparing ultrathin coatings.1, 33-36 PEG-bearing photoreactive groups have also been immobilized on surfaces by photocrosslinking.37 
Each of these strategies require the presence of specific surface functional groups and extensive optimization of the surface. Therefore, developing a versatile immobilization strategy that is capable of robustly anchoring polymers onto a variety of material surfaces is extremely important for biomedical and other bio-related applications. For this purpose, the inventors has reported extensively on the adhesive characteristics of 3,4-dihydroxyphenylalanine (DOPA), an important component of mussel adhesive proteins, to anchor PEG and peptides on a wide number of substrates, including noble metals, semiconductors, metal oxides, synthetic polymers, ceramics and composites surfaces.38-46 
The surface coverage and film thickness are two of the most important parameters influencing the antifouling performance of a PEG-coated surface. Groll and Gasteier et. al.1,33,34 reported that PEG films with thicknesses between 3 and 10 nm were not able to prevent non-specific cell adhesion under standard cell culture conditions (10% fetal calf serum). However, thicker star-shaped PEG films (15-50 nm) were able to prevent cellular adhesion under the same conditions. In addition, such films did not induce thrombocyte adhesion and exhibited very good hemocompatibility. In general, conventional antifouling coatings applied in thicknesses ranging from 15-50 nm are effective at reducing the attractive interactions between fouling species (cells/proteins/bacteria) and the underlying substrate.
Star-shaped PEG polymers have been previously employed for the preparation of hydrogel coatings through complicated methods involving substrate surface modification and polymer cross-linking by irradiation,47-51 or via reaction between the functionalized end-groups of the PEG stars.35, 52-54 In this invention, we describe a facile strategy to prepare PEG nano-hydrogel coatings with tunable thickness for antifouling applications. The polymer building block is comprised of four-armed PEGs modified with dihydroxyhydrocinnamic acid (DOHA). This catechol-containing molecule has a similar molecular structure as DOPA, and it shares the same adhesive characteristics. Despite employing a polymer composition that has been shown to be adhesive to biological constituents, a surprising and unexpected outcome was obtained in which hydrogel coatings derived from DOHA-derivatized PEG were actually an effective antifouling agent for proteins, cells and bacteria when applied to various surfaces.
Although the hydrogel coatings known from the existing art decrease cell and protein adsorption on surface to varying degrees, complex manufacturing methods for these coatings in many cases prevent wide usability. For example, conventional techniques require the use of reactive, costly, difficult to synthesize and handle coating materials; they require the use of costly irradiation units, or complicated adhesion promoters; and/or they require laborious coating processes.
Accordingly, a need exists for an antifouling hydrogel coating that can be anchored in stably covalent fashion onto multiple substrate surfaces and can be obtained in simple fashion. A need also exists to improve the manufacturing process of such hydrogel coatings, such that, in particular, the use of adhesion promoters can be dispensed with and coatings of long-term stability are nevertheless obtained. Such a hydrogel coating and methods of synthesis and use thereof would substantially simplify the coating process and open up a broad spectrum of applications, and is not known in the existing art.